Gaskets made of a metal material have been used to seal a joint where a cylinder head interfaces with a cylinder block of an engine. There are openings in the gasket which cooperate with the combustion chambers, water passages and oil passages in the engine. These gasket openings typically have a structure to enhance sealing around the openings.
Cylinder head gaskets are the most sophisticated type of gaskets. When first starting an engine in cold weather, parts near the combustion chamber might be subfreezing. Then, after only a few minutes of engine operation, these same parts may reach 400 degrees Fahrenheit. The inner edges of the cylinder head gaskets are exposed to combustion flame temperatures from 2,000 to 3,000 degrees Fahrenheit.
Pressures inside the combustion chamber also vary tremendously. On the intake stroke, a vacuum or low pressure exists in the cylinder. Then after combustion, pressure peaks of approximately 1,000 pounds per square inch (psi) occur. This extreme change from suction to high pressure happens in a fraction of a second. Cylinder head gaskets, under these conditions must also provide the following: seal intake stroke vacuum, combustion pressure, and the flame in the combustion chamber; prevent coolant leakage, resist rust, corrosion and, in many cases, meter coolant flow; seal oil passages through the engine block and engine head while resisting chemical action; allow for lateral and vertical head movement as the engine heats and cools; be flexible enough to seal minor surface warpage while being stiff enough to maintain adequate gasket compression; fill small machining marks that could lead to serious gasket leakage failure; and withstand forces produced by engine vibration.
Known ways to enhance gasket opening sealing includes the use of metal plates having wave beads. However, the gaskets with wave beads provide uneven sealing pressure patterns and shift the heavy load away from the desired wave area. When the heavy load is shifted away from the desired wave area onto a flat portion of the gasket, the sealing pressure is decreased. Moreover, this localized excessive loading accelerates the cracking failure at the flat portion of the gasket.
Therefore, there is a need for a cylinder head gasket that creates an even sealing pressure pattern at the wave area. It would be desirable to provide load shifting that reduces premature cracking failure by properly distributing the load along the wave area so that the load is not concentrated at the flat portion. The load should be distributed evenly throughout the entire region of the seal where the load is desired.